hard drive issuse and win 98

Ok here is the deal. I built a new computer and want to get some data off of an old hard drive that had Win 98 on it. I put the old hard drive into the new computer as a second drive. So both had win 98 on them but I was booting off the new one. After I copied the data I needed I put the old hard drive back into the old computer and tried to boot it, but it would't. It acted like windows didn't exsist on the drive. Does this sound Like an issue from putting in the new computer as a 2nd drive? if so can I fix it without reinstalling?

thanks
Dwhy